Insulin-like growth factor I (IGF-I) is a 70-amino-acid polypeptide hormone having insulin-like and mitogenic growth biological activities (Rinderknecht (1978) J. Biol. Chem. 253:2769; Rinderknecht (1978) FEBS Lett. 89:283). This hormone enhances growth and/or survival of cells in a variety of tissues including musculoskeletal systems, liver, kidney, intestines, nervous system tissues, heart, and lung. Administration of IGF-I has been indicated for the treatment of a variety of conditions in humans and animals.
Various formulations of IGF-I have been made. See, for example, U.S. Pat. Nos. 5,126,324, 5,324,639, 5,324,660, 5,374,620, and 5,650,496; International Publication Nos. WO 94/15584 and WO 96/40776; copending application entitled “High and Low Load Formulation of IGF-I in Multivesicular Liposomes,” U.S. patent application Ser. No. 08/925,531, filed Sep. 8, 1997; copending application entitled “Injectable Formulation Containing Succinate,” U.S. patent application Ser. No. 60/080,008, filed Apr. 3, 1998; and copending application filed concurrently herewith entitled “Method for Producing Sustained-Release Formulations,” U.S. patent application Ser. No. 09/188,051.
Inclusion bodies containing IGF-I have been formed when IGF-I is expressed as a heterologous protein. See, for example, European Patent Nos. EP 123,228, EP 128,733, EP 135,094, EP 230,869, and EP 288,451. When incorporated into such inclusion bodies, IGF-I is in a generally misfolded and biologically inactive form, and must be reduced, refolded, and resolubilized into an active, solubilized form. See, for example, U.S. Pat. Nos. 5,288,931, 5,410,026, 5,663,304, and 5,756,672; and International Publication No. WO 91/02807.
Other methods of making highly concentrated forms of proteins involve use of protein solubilizers and precipitating agents such as salts, and/or various manipulations of solution conditions such as pH, temperature, ionic strength, and other techniques known in the art. These methods often lead to protein preparations that are undesirable because they are biologically inactive, are relatively dilute, and/or contain pharmaceutically undesirable salts or other agents.